Basic Anti-Alias Questions

[exingo@adobeforums.com]

1. Can someone just explain why I want to use Anti-Alias when making a
selection? I understand that it is supposed to make it blend easier with
surroundings, but what does that really mean?


2. When would you not want to use anti-alias?



Thanks!

[Phosphor@adobeforums.com]

No need for antialiasing when the edges of your selection are perfectly vertical and perfectly horizontal. Any deviation from 0°, 90°, 180° or 270°—even if only a small amount— should have antialiasing applied.

Unless you specifically WANT the jaggedy stairstepped look, you should use antialiasing for any selection that has rounded or diagonal edges.

[Scott_Falkner@adobeforums.com]

Antialiasing is a method to recreate a shape at a higher resolution as a bitmap, then downsample it, say 4 times, so each screen pixel corresponds to 16 enlarged pixels (4 times 4). 16 black pixels become one black pixel. 16 white pixels become one white pixel. 16 pixels that are a mix of black and white become a corresponding shade of gray.

Antialiasing works on text -- so long as yuou are using an outline font, paths, oval marquees, and the lasoo tool. A magic wand selection of an antialiased area with antialiasing on will simulate antialiasing by partially selecting the shaded pixels at the edge of the selection.

[Tim_Lookingbill@adobeforums.com]

Don't get this confused with feathering which allows width variance of anti-aliasing either starting from the middle of an edge and expanding outward equally on either side or from one side inward.

[Scott_Falkner@adobeforums.com]

Feathering actully has nothing to do with antialiasing, and does not care if your selection was antialiased.

Think of a selection as a grayscale image (that's what it is). Feathering is identical to blurring that image.

[Tim_Lookingbill@adobeforums.com]

Where is feathering terminology used in the tools of PS? Is it used in the Marque and Magic Wand tools? Where did I see where you could actually set the amount of pixels to feather from the edge of the selection? I'm probably getting confused in the terminology.

[Scott_Falkner@adobeforums.com]

You can have a selection make with the lasoo or marquee feathered by changing the tool options. You can also feather any selection with Select->Feather.

I like to work in the mask, by pressing Q to swith to quickmask. There, I can blur my selection selectively, feathering just the parts I want. Press Q to return to select mode and I'm in business.

[Tim_Lookingbill@adobeforums.com]

Great tip, Scott, thanks.

[Scott_Falkner@adobeforums.com]

Yeah, Quickmask is Photoshop's best kept secret.